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Research Papers

Unsteady Transition Phenomena at a Compressor Blade Leading Edge

[+] Author and Article Information
Alan D. Henderson

School of Engineering, University of Tasmania, Hobart, 7001, Australiaalan.henderson@utas.edu.au

Gregory J. Walker

School of Engineering, University of Tasmania, Hobart, 7001, Australiagreg.walker@utas.edu.au

Jeremy D. Hughes

 Rolls-Royce plc, Derby DE248BJ, UKjeremy.hughes@rolls-royce.com

J. Turbomach 130(2), 021013 (Mar 21, 2008) (10 pages) doi:10.1115/1.2751148 History: Received September 01, 2006; Revised October 05, 2006; Published March 21, 2008

Wake-induced laminar-turbulent transition is studied at the leading edge of a C4-section compressor stator blade in a 1.5-stage axial compressor. Surface hot-film sensor observations are interpreted with the aid of numerical solutions from UNSFLO , a quasi-three-dimensional viscous-inviscid flow solver. The passage of a rotor wake, with its associated negative jet, over the stator leading edge is observed to have a destabilizing effect on the suction surface boundary layer. This leads to transition closer to the stator leading edge than would have occurred under steady flow conditions. The strength of this phenomenon is influenced by the rotor-stator axial gap and the variability of individual rotor wake disturbances. A variety of transition phenomena is observed near the leading edge in the wake path. Wave packets characteristic of Tollmien-Schlichting waves are observed to amplify and break down into turbulent spots. Disturbances characteristic of the streaky structures occurring in bypass transition are also seen. Examination of suction surface disturbance and wake-induced transitional strip trajectories points to the leading edge as the principal receptivity site for suction surface transition phenomena at design loading conditions. This contrasts markedly with the pressure surface behavior, where transition at design conditions occurs remotely from leading-edge flow perturbations associated with wake chopping. Here, the local receptivity of the boundary layer to the wake passing disturbance and turbulent wake fluid discharging onto the blade surface may be of greater importance.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

University of Tasmania research compressor facility

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Figure 2

Cross section of the research compressor showing the midpassage blade row configuration with typical instantaneous wake dispersion pattern

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Figure 3

Measured stator blade surface velocity distributions (from (18))

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Figure 4

Unsteady flow field around stator leading edge (UNSFLO ). Vectors indicate perturbation from local time-mean velocity. Gray shading indicates fluid entropy relative to the maximum level at the wake center.

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Figure 5

Left: Temporal variation in dimensionless ensemble-averaged quasi-wall shear stress (⟨τq⟩∕τq¯). Right: Temporal variation in dimensionless skin friction factor (Cf∕Cf¯), medium load case (ϕ=0.675).

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Figure 6

Temporal variation in momentum thickness Reynolds number and shape factor from UNSFLO computations, medium load case (ϕ=0.675)

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Figure 7

Stator surface ensemble-averaged intermittency ⟨γ⟩ (shaded contours) and probability of instability wave occurrence (line contours) with superimposed particle trajectories at different proportions of local freestream velocity (adapted from (7)) and added neutral stability boundary predicted by the present study

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Figure 8

Predicted temporal variation in shape factor for LAG and SAG cases, medium load case (ϕ=0.675)

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Figure 9

Typical raw quasi-wall shear stress traces, IGV wakes in stator passage (a∕S=0.5)

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Figure 10

Typical raw quasi-wall shear stress traces, IGV wakes on stator blade row (a∕S=0.0)

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